Pressure process for preparing acetylene



Dec. 29, 1970 o. P. KECKLER ETAL 5 .PRESSURE PROCESS FOR PREPARING ACETYLENE Filed Nov. 1, 1968 Ill-I @QOQQOQ. 99mph A @6 @6 9b @696 Q6 Q6 Q6 Q Q Q. Q G m 8 INVENTORS DAVID P. KECKLER JOHN EDWARD LOEFFLER,JR.

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ATTORNEY United States Patent O US. Cl. 260-679 5 Claims ABSTRACT OF THE DISCLOSURE In the superatmospheric pressure production of acetylene by the partial oxidation of hydrocarbons in a flame reaction, there can be fed through a gas distributor, for reaction in a flame chamber, two separate gaseous materials, i.e., a reactant gas formed from a premixture of hydrocarbons and oxidizing gas, and also supplemental oxidizing gas. In elevated pressure operation, acetylene production is enhanced by feeding an auxiliary gas through the distributor, also directly into the flame chamber, which gas contains inert material, or substances capable of forming acetylene, or both. Such gas is introduced into the zones of aspiration in the flame chamber created by the premixed gas flowing into such chamber.

BACKGROUND OF THE INVENTION Typically, the heart of the apparatus wherein gaseous hydrocarbons are converted to an acetylene-containing gas, by partial oxidation plus pyrolysis, is a gas distributor interposed between a mixing chamber and a reaction or flame chamber. In the mixing chamber the hydrocarbon feedstock is blended with oxidizing gas. In the flame chamber the resulting premixed gas is partially oxidized in the presence of supplemental oxidizing gas and coincident therewith a portion of the hydrocarbon feedstock is converted to acetylene. Examples of such apparatus for performing this partial oxidation process have been disclosed in US. Pat. 3,121,616 as well as US. Pat. 3,285,707.

Thus it has been the practice heretofore to employ the gas distributor for the distribution of two separate gaseous systems directly into the flame chamber, i.e., premixed gases and also supplemental oxidizing gas. In the practice of the present invention, the gas distributor is employed in elevated pressure operation for delivering three separate gas systems to the flame chamber, i.e., the two discussed hereinabove plus an auxiliary gas stream of hydrocarbons or inert gas, or both.

Although not wanting to be bound to any particular theory, it is believed that in gas distributor operation, the flow of premixed gas into the flame chamber creates a zone of aspiration around the distributor port through which such premixed gas enters the flame chamber. In'continuous operation, this aspiration zone or stagnant" zone is continuously fed by gas from the flame chamber which backmixes into such zone. C'oincidentally the zone is continuously depleted by entrainment of gas from such zone into fresh premixed gas feeding from the distributor port into the flame chamber. The residence time, within the chamber, of backmixing gas is longer than for gas entering the chamber and sweeping directly through the chamber from the gas distributor.

Such increased residence time, especially in pressure operation, e.g., at reaction chamber pressures above about two atmospheres, results in uneconomical and extensive decomposition of product gasses, for example acetylene, contained in the backmixed gas. However, superatmospheric pressure operation is otherwise desirable as compared with about atmospheric or subatmospheric pres- Patented Dec. 29, 1970 "ice sure processes since increased heat recovery is permitted at higher pressure and smaller equipment and piping sizes may be employed. Also, since acetylene recovery can most always be achieved with enhanced efficiency by subsequent separation operation at pressures above atmospheric, maintaining the flame chamber at superatmospheric pressure assists in obviating subsequent compression of an acetylene-containing gas in downstream purification apparatus.

SUMMARY OF THE INVENTION Thus, it is an essential feature of this invention that the auxiliary gas enter the flame chamber through the gas distributor in a manner to suppress backmixing, i.e., enter the flame chamber within the zones of aspiration produced by the flow of the premixed gas from the distributor to the chamber. In such operation, retarded backmixing can provide for a reduction in the prolonged, deleterious decomposition of the total premixed gas entering the chamber and thus can provide, particularly at superatmospheric pressures, a highly desirable reduction in the formation of soot and by-product gasses. More importantly, it has been found that by suppressing backmixing at elevated pressures with an auxiliary gas which contains substances capable of forming acetylene in a flame reaction, the proportion of acetylene in the gas leaving the chamber can be desirably enhanced, e.g., in a typical operation, acetylene production can be boosted by more than 20 percent although the amount of additional reactable hydrocarbons introduced by the auxiliary gas is less than 20 percent of the total reactable hydrocarbons fed to the flame chamber.

Thus the present invention is an improvement in the partial oxidation process for preparing acetylene wherein the flame chamber is maintained at a superatmospheric pressure above about two atmospheres, which improvement comprises feeding an auxiliary gas into the flame chamber, from a gas distributor, into the zone of aspiration produced by the flow of premixed gas from such distributor, with the auxiliary gas issuing into such chamber at a velocity up to the velocity of the premixed gas flowing into the chamber, wherein such auxiliary gas comprises a preponderance of gaseous components selected from the group consisting of inert gaseous materials, saturated and unsaturated hydrocarbons having at least two carbon atoms, and mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly understand the practice of the present invention the attached drawings present one modification of apparatus which has been more fully described in US. Pat. 3,285,707, incorporated herein by reference, and which modified apparataus can be employed. for carrying out the practice of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, gas distributor delivery tubes 9 pass through a lower metal tube sheet 6 for discharge of premixed methane-containing gas and oxidizing gas into a flame chamber. In addition, to fill out the symmetry of the grouping of delivery tubes 9, coolant deflecting members, or baffles 19, are mounted on the lower tube sheet 6. From outlet ports 7 in supplemental oxidizing gas conduits 13, oxidizing gas is discharged towards the flame chamber. Interposed between the premixed gas delivery tubes 9 are auxiliary gas delivery tubes 17. Through these auxiliary tubes 17 auxiliary gas is introduced into the flame chamber and into the stagnant zones, or zones of aspiration, formed by the gas issuing into the flame chamber from the premixed gas delivery tubes 9. Cooling water enters through conduits 18 and flows over the lower metal tube sheet 6 and around the baffles 19, the premixed gas delivery tubes 9, and the auxiliary tubes 17 as well as downcomers, not shown, from the supplemental oxidizing gas conduits 13.

Referring to FIG. 2, premixed gas flowing from a mixing chamber, not shown, flows down distributor tubes 39 and issues from entry ports in the lower metal tube sheet 6 into the flame chamber 11. Mounted on the lower tube sheet 6 are hollow metal support members 12 acting as downcomers for carrying supplemental oxidizing gas from conduits 13. Auxiliary gas flows through conduit 15 into an auxiliary gas header 16 from which auxiliary gas flows down through delivery tubes 17 and issues through entry ports 8 into the flame chamber 11.

Cooling water is charged through conduit 18 and flows between a bafile plate 21 and the lower tube sheet 6 and then up between the baflle plate 21 and an upper tube sheet 22, finally flowing into a chamber 23 for discharge through an exit port 24. The baflle plate 21 interposed between the upper tube sheet 22 and lower metal tube sheet 6, respectively, thereby forms a double pass shelland-tube type heat exchanger surrounding the ends of the premixed gas distributor tubes 9 as Well as the ends of the auxiliary gas delivery tubes 17.

Referring to FIG. 3, mounted on the lower tube sheet 6 is a hollow metal support member 12 serving as a downcomer for supplemental oxidizing gas from conduits 13. The supplemental oxidizing gas flows from the conduit 13 ino tthe hollow support member 12 through outlet port 7 and then through feed tubes 4, contained in the lower tube sheet 6, for entry into the flame chamber 11.

The flame chamber zones, around the premixed gas entry ports 5, and thus the zones into which the auxiliary gas flows upon issuing into the flame chamber 11 through the auxiliary gas entry ports 8, are the stagnant zones, or the zones of aspiration, referred to herein. These zones need not have well defined boundaries, i.e., they can vary according to turbulence existing in the flame chamber as well as in accordance with the configuration of the premixed gas entry ports. During operation of the burner, the auxiliary gas, either a reactant gas, or inert gas, or reactant plus inert gas, issues into the flame chamber 11 through the entry ports 8 and is swept into the premixed gas flowing through the gas distributor entry ports 5 thus displacing gas otherwise backmixing from the flame chamber.

Preferably, for enhanced acetylene production, the auxiliary gas is virtually all reactable to acetylene by pyrolysis in the flame chamber. However, the auxiliary gas can be an inert gas or a mixture of inert gas plus reactant gas which mixture, for economy, typically contains less than about 25% by volume of inerts. Suitable inert gases for preparing such a mixture include nitrogen, steam, hydrogen, and recycle gas, i.e., virtually to completely acetylene-free gas from the downstream purification zone, which gas is then recycled through the auxiliary gas system back into the flame chamber.

The reactable gases for the auxiliary system, i.e., the gases capable of conversion to acetylene in the flame chamber, are saturated and/or unsaturated hydrocarbons having at least two carbon atoms since methane is not readily convertible to acetylene in the flame chamber when present in substantial amounts in the auxiliary gas. Preferably, for reduced byproduct production, ethane and/ or propane are employed, but suitable reactable sub- 4 stituents forming a part to all of the auxiliary gas additionally include naptha, gasoline, kerosene, and, including those mentioned specifically above, parafiinic hydrocarbons having at least two, but generally for economy, not substantially in excess of about 12 carbon atoms.

Advantageously, to avoid cooling of the premixed gases in the flame chamber, and to enhance acetylene production where the auxiliary gas contains reactable constituents, the auxiliary gas is preheated prior to entry into the flame chamber to a temperature between about 5001500 F. The velocity of the auxiliary gas entering the flame chamber should be below that of the premixed gas feeding into the flame chamber since a too rapid flow of auxiliary gas can increase the amount of such gas sweeping through the chamber without reaction. Preferably, for most eflicient suppression of backmixing, the ratio of the velocity for the auxiliary gas to the entering premixed gas is between about 0.2-0.7:1.

Typically, the amount of auxiliary gas entering the flame chamber constitutes only a minor portion of the total volume of gaseous materials fed to such chamber. Where such auxiliary gas is preponderantly an inert gas, not more than about 30 volume percent of the gas entering the reaction chamber is such auxiliary gas to avoid flooding of the reaction chamber with large amounts of unreactable material. Preferably, for suppressed backmixing without substantial flooding, the amount of an inert auxiliary gas is about 5-20 volume percent of the total gas entering the flame chamber. When the auxiliary gas is substantially a reactant gas, the volume ratio of the auxiliary gas to the premixed gas is between about 0.04-0.4:1. A ratio of less than about 0.04:1 can provide for insignificant enhancement in acetylene production as well as augmented amounts of undesirable by-products, while an auxiliary gas to premixed gas volume ratio of greater than about 0.4:1 can lead to the feeding into the flame chamber of substantial amounts of gas which merely sweeps through without reaction. For eflicient acetylene production, the methane-containing gas contains at least about 50 volume percent methane and for efliciency and economy preferably contains greater than about 60 volume percent methane.

Since the effects of backmixing are especially deleterious, and thereby especially obviated by the auxiliary gas feed, for flame chambers maintained at superatmospheric pressures above about two, and particularly three, atmospheres, such auxiliary gas feed is most particularly directed to flame chamber operations conducted above such elevated pressure. However, reaction zone pressures above about 15 atmospheres are typically not accompanied by a coincident enhancement in the desirable features provided by such superatmospheric pressure operation.

In order that those skilled in the art may more completely understand the present invention and the preferred methods by which the same may be carried into elfect, the following specific example is offered.

EXAMPLE A furnace as shown in FIGS. 1 and 2 is fed 1680 moles of gas per hour made up of 38% oxygen and the balance methane gas of 98 percent purity; 1% of the oxygen issues through the auxiliary oxygen feed tubes 4, and the balance, plus the methane gas issues through the primary gas distributor tubes 9. The gas is preheated to a temperature of 980 F. prior to entering the flame chamber 11 and such chamber 11 is maintained during reaction at a superatmospheric pressure of 3.8 atmospheres. Twenty volume percent of the flame chamber gases are recycled from a downstream purification zone to the auxiliary gas header 16 and subsequently back into the flame chamber in the zones of aspiration between the primary gas entry ports 5. This recycle gas enters the flame chamber 11 at a temperature of about 700 F. By such operation the pyrolysis gas after quenching shows an increase of 4 percent in the actylene produced based on the total acetylene production without recycle.

The furnace thus described is subsequently operated in a similar manner but instead of recycling gas from the purification zone through the auxiliary gas entry system, 110 moles per hour of 91% pure ethane, with a balance of virtually all inert gas, are fed through the auxiliary gas delivery conduits 17 into the reaction chamber 11, which ethane is preheated at a temperature of 900 F. The resulting pyrolysis gas after quenching shows an about 30.5% increase in the acetylene produced, basis total moles of acetylene produced, as well as a desirable increase in the acetylene content of the burner outlet gas of more than 2.5%, both calculated on a dry gas basis.

It is to be understood that, although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

We claim:

1. In a process for preparing acetylene from a methanecontaining gas by incomplete oxidation at superatmospheric pressure wherein said gas is mixed with an oxidizing gas in a mixing chamber, thereafter the resulting premixed gas flows through a gas distributor into a flame chamber maintained at superatmospheric pressure above about two atmospheres, and supplemental oxidizing gas flows from said gas distributor into said flame chamber, the improvement which comprises feeding an auxiliary gas into said flame chamber from said gas distributor and into the zone of aspiration produced by the flow of said premixed gas from said gas distributor, said auxiliary gas issuing into said flame chamber at a velocity up to the velocity of said premixed gas flowing into said flame chamber, wherein said auxiliary gas comprises a preponderance of gaseous components selected from the group consisting of inert gaseous materials, saturated bydrocarbons having at least two carbon atoms, unsaturated hydrocarbons having at least two carbon atoms, and mixtures thereof.

2. The process of claim 1 wherein said methane-containing gas contains in excess of about volume percent methane and the volume ratio of said auxiliary gas to said methane-containing gas is between about 0.04 04:1.

3. The process of claim 1 wherein said auxiliary gas is substantially a substance selected from the group consisting of naphtha, gasoline, kerosene, paraflinic hydrocarbons having from 2 to 12 carbon atoms inclusive, and mixtures thereof.

4. The process of claim 1 wherein said auxiliary gas is substantially a gaseous substance selected from the group consisting of nitrogen, steam, hydrogen, recycle gas and mixtures thereof.

5. The process of claim 1 wherein the flame chamber is maintained at a pressure between about 215 atmospheres, said auxiliary gas is preheated to a temperature between about 500l500 F. prior to feeding into said chamber, and the ratio of the velocity of said preheated gas entering said flame chamber to the velocity of the premixed gas entering said chamber is between about 0.2-0.7:1.

References Cited UNITED STATES PATENTS 2,889,209 6/1959 Hale 260679 2,705,189 3/ 1955' Ekholm- 23209.4 3,287,090 11/ 1966 Loeflier, Jr. et al 23277 3,176,046 3/1965 Kondo et al. 260679 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner U.S. Cl. X.R. 23-277 

